This proposal seeks a better understanding of how sympathetic cardiovascular and vasomotor activity is generated and, hence, how cardiovascular function is regulated by the central nervous system. The long goals of these studies are (1) to know more about the normal physiology of the autonomic nervous system in order to improve our understanding of many autonomic imbalances secondary to other pathologies, e.g., congestive heart failure, shock, etc., and (2) to gain a better approach to the physiopathology and treatment of essential and neurogenic hypertension. Neurons in the rostral ventrolateral medulla (RVLM) are critically involved in the tonic and reflex control of the circulation. These neurons are able to be characterized because: a) they receive baro- and mechanoreceptor inputs, b) they project to the sympathetic spinal cord, c) they are most probably the origin of the tonic vasomotor activity, and d) they mediate the baro- and other mechanoreflex responses. The major aim of this proposal is to test the hypothesis that the activity f a characterized group of RVLM-spinal neurons, responsible for generating tonic and reflex sympathetic cardiovascular activity is modulated by projections originating in the contralateral RVLM. Using an intracellular recording technique in vivo, we have identified different types of RVLM neurons with electrophysiological and cardiovascular (barosensitive) characteristics and projections to the sympathetic spinal cord. Study I in this proposal is designed to provide with new significant data to anatomically characterize the interconnecting pathways between both RVLMs. This information will further support Study II that is designed to test a model of sympathetic cardiovascular regulation incorporating the reciprocal innervation of RVLM neurons. This research will produce evidence that synaptic inputs (excitatory or inhibitory) received from the opposite RVLM neurons. We will further investigate the hypothesis that these presumed inputs are conveyed by projections originating in C1 adrenergic neurons located in the opposite RVLM. Overall, these studies will provide new information about the neuronal mechanisms in the RVLM involved in the tonic and reflex control of cardiovascular function, particularly the possible role played by the reciprocal RVLM adrenergic projections.